1. Field of the Invention
The invention relates to a composition for purifying gases, in particular effluent air, which are conducted through a bulk volume of the composition. The bulk volume is thereby populated with micro-organisms.
2. Description of the Related Art
German publication DE-U 92 16 668 discloses a bulk filter for biological gas filters containing grapeseeds and minerals. While the bulk material is essentially suitable for removing highly odorous noxious components from the gases, it has been found that it takes rather a long time after starting the process before the filter reaches its full purifcation rate. Additionally, the purification rate is less than satisfying even after that time.
German patent publication DE-A 43 04 190 discloses a process and a device for the purification of gases; the gases to be purified are thereby conducted through a bulk volume of organic material. As an organic material there is proposed peat-heather-mixtures, bark chips, wood splinters, compost or also other mixtures of peat/synthetic material, compost/synthetic material or the like. In order to obtain a sufficient capacity of the biofilter it is necessary to feed the micro-organism populating the organic layer with nutrient substances. As a quite undesired side-effect, however, unwanted micro-organisms are supported as well, which have to be suppressed by adding toxic agents. Therefore the operation of such a biological filter is elaborate and depends from a precise control and regulation. Furthermore, the use of toxic agents is risky for obvious reasons of environmental protection.
German patent publication DE-A 041 233 discloses a process eliminating odoriforous substances from exhaust gases with the use of fibrous peak and heather. The efficiency of the filter in that process is improved in that the material is placed in a rotating cylinder. That prior art process, therefore, requires elaborate mechanical components and it cannot be used in an economical fashion for various applications.
European patent publication EP-A 492 135 discloses a device for purifying air, in which filter beds populated with micro-organisms are disposed in a purification column. Bark chips are described as a filter bed. Elaborate humidification equipment is required in order to obtain adequate and acceptable purification efficiency.
Further biological filters are described in German patent publication DE-A 41 02 167, in European patent application EP-A 497 214 and in U.S. Pat. No. 5,232,676 (EP-A 470 468). However, similar disadvantages as described above are encountered with those processes and devices.